The present invention relates to bigraft copolymers having a polyhydrocarbon backbone containing allylic chlorines and bromines and grafts of two monomers, preferably selected from the group consisting of monovinyl aromatic compounds and isoolefins. The invention also relates to a process for the preparation of the bigraft copolymer described herein.
It is known that certain alkylaluminum compounds in conjunction with suitable polymer halides will initiate the cationic polymerization of many various olefins, e.g., isobutylene, styrene, isoprene, butadiene and the like. Two references which disclose such polymerizations are U.S. Pat. Nos. 3,904,708 and 3,933,942. Given the above-referenced knowledge, one could expect to graft a suitable olefin onto a polymer backbone such as poly(ethylene-propylene-diene) (EPDM) which carries the requisite halogen functionality and, in fact, this work has been performed and the products, appearing as typical thermoplastic elastomers, have been studied.
Notwithstanding the present state of the art, we have found the literature to be devoid of teaching directed toward the cationic grafting of two different olefins onto EPDM rubber. This state of the art is believed to be attributable to the fact that the principle of selective sequential cationic initiation has not been known.